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NSW killer jailed for brutal murder of mum

Family and friends of murdered NSW mother-of-four Renee Mitchell are "devastated" her killer, Graham Anthony George Sloane, could be out of jail in 16 years.

Sloane was sentenced to a minimum 18 years in the Newcastle Supreme Court on Thursday but, factoring in time already served since his arrest in 2014, he could be released in 2032.

Family spokesman Jake Kevill says Ms Mitchell's husband, Dale, and their sons are angry the murderer could one day walk free.

"They wanted life," he told reporters outside court.

"(Mr Mitchell) just wanted to say he's not happy with the verdict - he'd rather he (Sloane) be in longer."

Another family member, who did not want to be identified, said the whole family was "absolutely devastated".

Sloane, 69, was found guilty in January of stabbing to death Ms Mitchell near the car park of a bush reserve just a few hundred metres from her home in the Lake Macquarie suburb of Windale, south of Newcastle on November 11, 2014, and leaving her body where it laid.

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Handing down the sentence, Justice Helen Wilson said Sloane's attack was "brutal and pitiless", and the former army sergeant had shown no remorse or contrition for his "terrible crime".

Jurors during the one-week trial rejected the defence assertion that Sloane should only be found guilty of manslaughter due to an "abnormality of the mind" at the time of the killing.

Justice Wilson said there was no dispute Sloane suffered from bipolar disorder at the time of the offence but "it is its severity and its relevance ... that is in question".

Sloane had known Ms Mitchell for several years through her job as an aged-care nurse, but their friendship soured, and Justice Wilson said it was not clear how he coerced her into leaving her home half-dressed and with her children out the back after he turned up uninvited on the evening of her death.

"I am satisfied, however, that Mrs Mitchell left the house under some form of compulsion from the offender," she said.

Justice Wilson described how Sloane drove Ms Mitchell the short distance to the reserve, where she likely tried to escape before he attacked with a knife that was never found. Its blade would have been at least 15 centimetres long.

Ms Mitchell, 38, suffered 16 wounds, five of which were deemed "significant" during an autopsy. They included two deep stab wounds to the heart and one to her neck.

Medical evidence presented during the trial showed those wounds were so severe Ms Mitchell could have survived only "for minutes at best".

"Mrs Mitchell must have been terrified and in pain during this savage assault," Justice Wilson said.

Various medical and psychological assessments after Sloane's arrest concluded he was "disconnected from reality" and displayed a combination of depressive and hypo-manic symptoms.

However, Justice Wilson said that from the evidence presented, it was apparent he had deliberately misled investigators and doctors and was still able to control his actions.

"He simply chose not to," she said.

Therefore, his moral culpability for the murder was not significantly lessened by his mental illness.

Sloane is no stranger to the jail system. He was jailed for eight years in 1997 for manslaughter after strangling to death his then-mother-in-law, Barbara Wilson, 72, but was released on parole after five years.